1. Field of the Invention
The present invention relates to rotary valves in which the stem reciprocates relative to the closure member and in which the stem is connected to the closure member so that when the stem rotates, the closure member and the stem rotate together. The improvement consists of a rotary valve with negligible dead cavity space in the valve body and a valve that automatically self-adjusts for wear of the sealing surfaces and maintains sealing integrity independent of fluid pressure. In one embodiment,the stem back-seats to reduce fugitive emissions.
2. Brief Description of Prior Art
In a rotary valve the closure member is rotated between the valve closed position and the valve open position. The rotation of the closure member is done with the help of a stem connected to the closure member. In a ball valve, the stem only rotates and does not reciprocate. In a rotary tapered plug valve, e.g. a sleeve-lined plug valve, the stem also rotates and does not reciprocate. In a tapered plug valve where the plug lifts, rotates and then reseats onto the valve body seats, the stem,which is integrally connected to the plug, rotates as well as reciprocates with the plug.
A valve assembly has a valve body having a body cavity. Due to the nature of the assembly to achieve sealing integrity, there remains some dead cavity space in the valve body of a ball valve. In a tapered plug valve in which the plug lifts, rotates, and then reseats onto the valve body seats, there also remains some dead cavity space to allow for the lifting of the plug. However, when the plug is lowered onto the valve body seats, suspended particles in the fluid medium get trapped between the plug and the seating surfaces, thereby compromising sealing integrity. So a lifting plug type of valve can be used only for clean fluids without suspended particles in fluid. In many of the valves that are in use today, the sealing integrity is compromised when the sealing surfaces wear out with valve usage and the valve starts to leak. The dead cavity space in a valve body contributes to the accumulation of debris in the body cavity. This is particularly disadvantageous for sanitary applications of the valve. These are some of the disadvantages of the valves currently in use today.
Therefore there exists a need today for a valve with negligible dead cavity spacein the valve body, and for a valve that automatically self-adjusts for wear of the sealing surfaces and maintains sealing integrity independent of fluid pressure. There also exists a need today for a valve that can be used with clean fluids as well as with fluids with suspended particles, e.g. slurry.
In valves that are in use today, only non-rotary valves with reciprocating stems are provided with back-seats that can be loaded with externally variable stem seating force. So far it has been found very difficult and elusive to provide back-seats on rotary valve stems to prevent fugitive emissions. The current method of containing fugitive emissions in rotary valves is to put the stem packing under "live loading" with springs which provides a constant compressive force on the stem packing. This compressive force is not automatically self-adjusting.
Therefore, there exists a need today in which rotary valves could be provided with back-seats for the stem whereby the back-seating force automatically self-adjusts for wear of the seating surfaces independent of fluid pressure, in order to prevent fugitive emissions and not just to contain them as is the case with live loading of stem packing.